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Re: Unnecessary scan on a partial index slows down query dramatically

From: "Jimmy Choi" <yhjchoi(at)gmail(dot)com>
To: "Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: pgsql-general(at)postgresql(dot)org
Subject: Re: Unnecessary scan on a partial index slows down query dramatically
Date: 2008-04-25 16:29:48
Message-ID: 5770602b0804250929j413c4893j60c7c1d69c7850d5@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-general
Thanks. I'm not really in a position to upgrade at the moment. I guess
in the short-term I'll tweak the query to work around this (e.g.
removing "status = 3" or adding more refining conditions both seem to
work).

Please let me know if there are configuration settings I should try.

Thanks,
Jimmy


On Fri, Apr 25, 2008 at 12:13 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> "Jimmy Choi" <yhjchoi(at)gmail(dot)com> writes:
>  > A simple query is executing much slower than expected. When looking at
>  > the query plan, I see a bitmap index scan on a partial index that does
>  > not have any associated index condition. How could that happen?
>
>  Easily --- it thinks that the partial index predicate is useful in
>  itself.
>
>
>  > "vacuum analyze" doesn't solve the problem. I'm running 8.1.5.
>
>  choose_bitmap_and was rewritten (again) in 8.1.9.  Try a newer
>  version.
>
>  http://archives.postgresql.org/pgsql-committers/2007-04/msg00233.php
>
>                         regards, tom lane
>
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Subject: Re: Unnecessary scan on a partial index slows down query dramatically
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